One of the enduring mysteries of the Obama presidency is why he keeps leaning far left when independent voters make it clear they want a centrist in the White House. It is not an academic point — independents swung the 2008 election his way, and without them, Obama probably can’t win a second term.

Well, consider the mystery solved. The reason Obama keeps tilting left is that so many independents have dumped him and he has almost no chance of getting them back. So energizing libs for a massive turnout is his next-best hope.

The bad news for the president is pronounced in a Bloomberg news poll. Only 29 percent of independents approve of his performance on the economy, while 66 percent disapprove.

On reducing deficits, a prime issue for independents, 25 percent like what he’s doing, while 67 percent don’t. Only 30 percent support his job-creation ideas and 34 percent his health-care plans.

Here’s the killer: 46 percent of independents say they definitely won’t vote for him again, while only 21 percent say they will. By comparison, in 2008 he got 52 percent of independent voters.

The numbers explain what, on the surface, doesn’t make any sense. Against the backdrop of high unemployment and sluggish growth, and with a large majority of Americans wanting smaller government and deficit reduction, the president keeps going in the opposite direction. He’s pushing more spending, big tax hikes and more regulation — measures that would almost certainly make the economy worse just as voters are going to the polls.

While his record shows Obama believes in those ideas, the political calculation is even more obvious.

Without independents, he must turn out very high percentages of the party’s base — young people, blacks, Latinos, unions and white liberals. He panders again and again on tax-and-spend because that’s what those voters worship.

It’s a “me first” strategy that puts his job hopes over those of the 25 million Americans wanting full-time work. But even that desperate effort is not going well.

The Bloomberg poll finds that, of those who supported Obama before, 37 percent say their support has waned and 19 percent say they no longer support him.

The upshot is that Obama is in a box of his own making. The jobs speech didn’t give him a bounce and, in addition to Republican opposition to the proposals, key Democrats in the Senate are openly balking. As a package, his proposals are dead.

There is one hope left for Obama: the GOP. If the Republican nominee also turns off independents, the president will be back in the hunt.

He will employ — we’ve seen shades already — a scorched-earth negative campaign. He’ll fear-monger about “extreme” GOP agendas, especially toward the elderly and the poor.

And surrogates will play the race card. Indeed, that, too, has already started, with the claim that critics are not giving Obama the “respect” other presidents enjoyed. In this case, “respect” is a code word for race.

That could work — if millions of Americans come down with amnesia and forget the brutal pounding President George W. Bush took. A favorite charge against Bush was that his policies were un-American. Here’s an example:

“The way Bush has done it over the last eight years is to take out a credit card from the Bank of China in the name of our children, driving up our national debt from $5 trillion for the first 42 presidents . . . so that we now have over $9 trillion of debt that we are going to have to pay back — $30,000 for every man, woman and child. That’s irresponsible. It’s unpatriotic.”

Barack Obama said that in 2008. Three years later, the debt is $14 trillion and jobs are shrinking. Pound away, America.

Bikes & $$ hikes? Yikes, it’s Mike!

When I first saw the headline that Mayor Bloomberg had warned of “chaos in the streets,” my heart raced. Maybe he finally realized his bicycle obsession had gone too far and would lead to open rebellion in Gotham.

No such luck. The rebellion over bike madness might happen, but Bloomy won’t see it coming.

He sees only what he wants to see. His latest “vision” is that New York needs 10,000 more bikes. Yikes.

On one level, it makes sense. He built miles of bike lanes and hardly anybody uses them. So he’s got to find users. Otherwise people will start saying crazy things, like that the lanes, at a price of tens of millions of taxpayer dollars and increased congestion, don’t make sense. Imagine that.

The Big Idea of his third term is that cars are bad. That also explains his support for the Port Authority’s crushing toll hikes.

Cash tolls on the George Washington Bridge, Holland and Lincoln tunnels and other PA crossings will go from $8 to $12 today. E-ZPass holders will pay $9.50 during peak periods.

The mayor said Friday that “some businesses and some people” would be hurt, but added: “On the other hand, if one of the bridges falls down, how would you feel about that for the economy?”

Apart from the fact that Bloomy never met a tax hike or fee he didn’t like, his defense of the toll hikes is half-baked. The cost of keeping the crossings sound is a fraction of the money being raised. The real hole in the PA budget is the World Trade Center and other real estate operations.

Motorists — which is to say, people mostly involved in commerce — are getting stuck with the bill only because they’re a captive audience. Everything else is a fiction wrapped inside a scare tactic about falling bridges.

Liberal solar flares

A statement from the National Resources Defense Council gets all huffy about Solyndra, the solar-panel firm that went bust, fired 1,100 workers and burned through $535 million of fishy loans it got from the White House.

“We didn’t pull the plug on Edison when the first light bulb blew out,” the statement says. “We didn’t close up shop when the first Ford got a flat tire. And we’re not about to give up on the solar industry and the vital jobs it creates.”

Oh, put a sock in it. Edison and Ford didn’t get gazillions in taxpayer handouts.

Koch not done with O

Ed Koch isn’t finished stirring the pot. Fresh off his winning gambit to make the race to succeed Anthony Weiner into a protest vote against President Obama’s hostility toward Israel, Democrat Koch is threatening to go to Florida to talk to Jewish voters there if Obama doesn’t change course. I’d say Koch better start packing. Obama sees the Palestinians as oppressed and Israelis as the oppressors, and he won’t let facts get in the way of his warped worldview.

Overexposure

Whoever hacked Scarlett Johansson’s cellphone and sent nude pictures of her around the Internet is a creep.

But that’s obvious. What’s less obvious is why she kept nude photos of herself on her phone.